Line hydrophone



Nov. 15, 1966 G. T. ALDRICH 3,286,227

LINE HYDROPHONE Filed Feb. 20, 1953 wz owv United States Patent 3,286,227 LINE HYDROPHONE Gerard T. Aldrich, Waterford, Conn., assignor to the United States of America as represented by the Secretary of the Navy 1 Filed Feb. 20, 1953, Ser. No. 338,175 7' Claims. (Cl. 340-13) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor. I

The present invention concerns a hydrophone. In particular the invention concerns a line hydrophone that makes use of a stack of alternate active-element cylinders and isolator cylinders that isolate from shock, vibration and sound; the stack is also isolated from shock, vibrations and sound of the vessel in which the line hydrophone is mounted.

The active elements of line hydrophones may be. composed of piezoelectric ADP or Rochelle-salt crystals, magnetostrictive materials, or electro-strictive. ceramics such as barium titanate. In the prior art such hydrophones customarily have been mounted upon frames of metal rods and housed in pressureproof boots.

In one prior art construction a small expendable line hydrophone. has been constructed from active-element cylinders stacked end to end and held. togetherbytwo end pieces fastened to a single threaded metal rod mounted concentrically along thelongitudinal axis of the cylinders. This hydrophone construction is satisfactory for expendable units. However, this construction is far from satisfactory for hydrophones designed for shipboard use because there results a reduction in sensitivity and because for shipboard use such factors as strength, rigidity, and mounting are critical. These critical factors make impossible the construction for shipboard use of hydrophones three feet long or longer by such method. In addition, because the elements of the expendable hydrophones are not separated and isolated from each other, some shock, vibration and acoustic short circuiting occurs. Moreover, there is not provided shock, vibration and acoustic isolation against own-ship vibration; if one element is excited by a local noise, the remaining elements are similarly affected.

It is an object of the invention to provide a line hydrophone.

Another object is to provide an inexpensive directional hydrophone that is suitable for sonar applications.

Another object is to provide a low-impedance, highcapacitance, acoustic generator which can be used with relatively long lengths of standard cable without causing the generated voltage to be attenuated seriously.

Another object is to eliminate phase and amplitude response as functions of the orientation of the hydrophone.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

The single figure is a perspective view of a preferred embodiment of the invention with parts broken away for clarity of illustration.

There is shown a hydrophone comprising a square brass contact rod 10 nested in a longitudinal surface slot 11 milled in a round stiffener rod 12 of acoustic isolator material such as Formica or wood. Small screws 9 hold the square brass contact rod 10 in place. The round Formica stiffener rod 12 is wrapped with an acoustic isolator blanket 13 of material such as rubber 3,286,227 Patented Nov. 15, 1966 having non-connected cells, an example of such material being Celtite. Absorber blanket 13 has a longitudinal opening that exposes square biass contact rod 10. Ten

electrically connected in parallel by a longitudinal fia-t brass strip 16 soldered in two places 18 to the outside ofeach barium titanate cylinder 14 and by two small wires 17 soldered to the inside of each barium titanate cylinder 14 and to the square brass contact rod 10. Polystyrene end spacers 21 and Celtite end spacers 22 are fitted on round Formica stiffener rod 12. A brass endplug 23 is secured at one-end of round Formica stitfener rod 12 by set screws 24; a brass cable end fitting 25 is fitted at the other end. A cable 26 including a pair of electric conductors 27 and 28 is connected to the square brass contact rod 10 and to the flat brass strip'16. A. porosity-free neoprene rubber boot 29 that is. moistened on the inside with castor oil isdrawn over 'the assembly. A rubber seal 31 and a clamp plate 32 are mounted in place and held there with nuts 33 and lock. washers 34. The assembly is evacuated and, if desired, filled with castor oil. A pipe plug 35 is screwed into the brass end plug 23 and a brass restraining tube 36 is forced over the neoprene rubber boot 29.

In operation, acoustic energy transmitted through the water impinges upon the barium titanate cylinders 14 and is converted into electrical energy which is transmitted through the cable 26 to conventional electronic equipment (not shown) providing for either audio or visual presentation of the received signal.

This hydrophone has the advantage of being inexpensive to manufacture. The acoustic insolator cylinders 15 between the barium titanate cylinders 14 provide protec tion against undesirable shock, vibration and sound being transmitted from one barium titanate cylinder 14 to others in the hydrophone. This feature has not appeared in previous. designs of line hydrophones. Because of blanket 13 the individual barium titanate cylinders 14 are isolated against shock, vibration and sound which in other hydrophones have been transmitted through the supporting assemblies. The neoprene rubber boot 29 not only offers protection. from shock and vibration but also facilitates the transmission of sound to barium titanate cylinders 14.

The frequency response from the hydrophone is good in contrast with magnetostrictive hydrophones in which response characteristics are poor. The impedance of the hydrophone is low in contrast with crystal hydrophones which have high irnpedances.

Because the sensitivity of the barium titanate cylinders 14 is good, there is no need for transformers which cause phase distortion. This is especially important when two or more hydrophones are used for the purpose of phase comparison.

Inasmuch as the barium titanate cylinders are cylindrical, equi-phase and equi-amplitude response is provided.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

I claim:

1. A hydrophone comprising a stiff first rod, said first rod having a longitudinal surface slot, an electric conductor second rod nested in the slot, a blanket wrapped about said first rod, said blanket having a longitudinal opening exposing said second rod, a stack of cylinders mounted coaxially on said blanket, said cylinders including alternate active elements and spacers, means electrically connecting the inside of each element with said second rod, a longitudinal electric conductor strip outside said stack, means electrically connecting the outside of each element with said strip, and a sound-transparent and impervious boot inclosing said stack.

2. A hydrophone as defined in claim 1 in which said stiff first rod is formed of Formica, said electric conductor second rod is formed of brass, said blanket is formed of shock and vibration and acoustic isolator material, said spacers are formed of polystyrene, said longitudinal electric conductor strip is formed of brass, and said boot is formed of porosity-free rubber. I

3. A hydrophone component comprising a stiff first rod, said first rod having a longitudinal surface slot, an electric conductor second rod nested in the slot, a blanket wrapped about said first rod, said blanket having a longitudinal opening exposing said second rod, a stack of cylinders mounted coaxially on said blanket, said cylinders including alternate active elements and spacers, means electrically connecting the inside of each element with said second rod, a longitudinal electric conductor strip outside said stack, and means electrically connecting the outside of each element with said strip.

4. A hydrophone component as defined in claim 3 in which said stiff first rod is formed of Formica, said electric conductor second rod is formed of brass, said blanket is formed of shock and vibration and acoustic insolator material, said spacers are formed of polystyrene and said longitudinal electric conductor strip is formed of brass.

5. A hydrophone for use on ships and other places where the transducer part should be free from shock, vibrations and sound from the support on which it is carried, which comprises an elongated, rigid stiffening member, vibration isolating means surrounding and in contact with said member, a plurality of cylinders of electrostrictive material surrounding and mounted approximately concentrically on and supported by said isolating means and arranged end to end therein in spaced apart relation, spacers of vibration isolating material interposed between said cylinders on said isolating means and each abutting end to end with both'adjacent ends of said cylinders which it separates, end elements secured to the ends of, and of greater diameter, than said member, a multiwire cable passing in water-tight manner through one ,of said elements, means connecting the ends of said wires of said cable, one to the outer faces of said cylinders and another to the inner faces of saidv cylinders, and an acoustically transparent, moisture impervious boot extending between, and coupled water-tight to, said end elements and surrounding and enclosing said end elements, said isolating means, said spacers and said cylinders.

6. A hydrophone for use on ships and other places where the transducer part should be relatively free from shock, vibrations and sound from the support on which it is carried, which comprises an elongated, rigid, stiffening member, a plurality of cylinders of electrostrictive material arranged in end to end alignment, but spaced apart, and through which said member extends, acoustic isolating means interposed between said member and said cylinders fitting the space between them, and supporting said cylinders, vibration isolating, spacing means interposed between and abutting adjacent both adjacent cylinder ends between which they are disposed and keeping said cylinders in said spaced apart relation, end elements secured to the ends of, and of greater diameter than, said member, an acoustically transparent, moisture impervious boot extending between, and coupled water-tight to, the exterior periphery of said end elements and forming with the end elements a closed envelope around and snugly fitting said cylinders, wires having water tight entry into said envelope, and means electrically connecting one wire to the outer faces of said cylinders and another to the inner faces of said cylinders, whereby said cylinders will receive or transmit sounds through said boot, and have minimum sensitiveness to sounds, vibrations and shock from the support on which said envelope is mounted.

7. A hydrophone for use on ships and other places where the transducer part should be free from shock, vibrations and sound from the support on which it is carried, which comprises an elongated, rigid, stiffening member, vibration isolating means snugly surrounding and in contact with the periphery of said member for the major portion of its length, a plurality of hollow cylinders of electrostrictive material surrounding, mounted on, and supported by said isolating means and arranged in end to end but spaced apart relation therein, a spacer of vibration isolating material interposed between and abutting, at its ends, with each adjacent cylinder end and of approximately the same radial thickness as said cylinders, end elements secured to the ends of, and having cylindrical peripheries, an elastic moisture impervious, acoustically transparent, electrically non-conducting boot surrounding said cylinders and cylindrical peripheral parts of said end elements to form a moisture tight enclosure around said cylinders, and two conductive means entering said enclosure and connected respectively to the inner and outer faces of said cylinders.

References Cited by the Examiner UNITED STATES PATENTS 2,417,829 3/1947 Keller 340l0 2,434,648 1/1948 Goodale 340-10 2,486,560 11/1949 Gray 34010 2,732,536 1/1956 Miller 3408 2,772,405 11/1956 Schurman et a1 340-10 2,837,731 6/1958 Harris.

FOREIGN PATENTS 818,828 10/1937 France.

CHESTER L. JUSTUS, Primary Examiner.

NORMAN H. EVANS, FREDERICK M. STRADER,

Examiners.

J. R. SPALLA, M. A. MORRISON, C. F. ROBERTS,

J. P. MORRIS, Assistant Examiners. 

1. A HYDROPHONE COMPRISING A STIFF FIRST ROD, SAID FIRST ROD HAVING A LONGITUDINAL SURFACE SLOT, AN ELECTRIC CONDUCTOR SECOND ROD NESTED IN THE SLOT, A BLANKET WRAPPED ABOUT SAID FIRST ROD, SAID BLANKET HAVING A LONDITUDINAL OPENING EXPOSING SAID SECOND ROD, A STACK OF CYLINDERS MOUNTED COAXIALLY ON SAID BLANKET, SID CYLINDERS INCLUDING ALTERNATE ACTIVE ELEMENTS AND SPACERS, MEANS ELECTRICALLY CONNECTING THE INSIDE OF EACH ELEMENT WITH SAID SECOND ROD, A LONGITUDINAL ELECTRIC CONDUCTOR STRIP OUT SIDE SAID STACK, MEANS ELECTRICALLY CONNECTING THE OUTSIDE OF EACH ELEMENT WITH SAID STRIP, AND A SOUND-TRANSPARENT AND IMPERVIOUS BOOT INCLOSING SAID STACK. 